The present invention relates to a catalyst for hydrotreating hydrocarbon containing feeds including at least one noble metal from group VIII and silicon as a doping element.
Petroleum cuts, and in particular bases for fuels, gasolines, kerosines and gas oils, contain aromatic compounds the concentration of which has to be further and further reduced under new or future legislation limiting the amount of aromatic compounds in the above fuels.
Current processes for hydrogenating aromatic compounds in solvents or aromatic petroleum cuts such as kerosines or gas oils use noble metal type catalysts, for example platinum, deposited on an alumina support with a high specific surface area. However, such metals are highly sensitive to poisoning by sulphur-containing and nitrogen-containing compounds present in the feeds and thus such feeds have to be desulphurised and denitrogenated to a very great extent before treating them using a catalyst based on a noble metal.
It is thus important to produce aromatic compound hydrogenation catalysts in solvents or in aromatic petroleum cuts such as kerosines and gas oils which are highly active in the presence of sulphur and/or nitrogen and/or oxygen so as to reduce the severity of prior hydrotreatment and to achieve even higher degrees of hydrogenation.
Catalysts based on platinum and palladium have been described for the properties for hydrogenating aromatic compounds. In the case of using an alumina type support (U.S. Pat. No. 3,943,053), it is reported that it is necessary to precisely control the metal contents, as well as the preparation conditions. The use of supports based on silica-alumina has also been reported. Examples are U.S. Pat. Nos. 4,960,505, 5,308,814 and 5,151,172. Those catalysts are based on a highly specific zeolite and have the disadvantage of requiring selective deposition of noble metals onto the zeolite.
The present invention relates to a catalyst including at least one noble metal from group VIII (group 8, 9 and 10 in the new notation for the periodic table: Handbook of Chemistry and Physics, 76th edition, 1995, inside front cover), i.e., at least one metal selected from ruthenium, rhodium, palladium, osmium, iridium and platinum, associated with a porous matrix. The catalyst is characterized in that it includes silicon as a doping element. The catalyst also optionally includes boron, optionally phosphorous, optionally at least one group VIB element (group 6) and optionally at least one group VIIA element (group 17, the halogens).
The present invention also relates to processes for preparing the catalyst, and to its use in petroleum cut refining processes.
More particularly, the catalyst of the present invention can be used for hydrogenating aromatic compounds or for dearomatisation of aromatic compounds, or to reduce aromatic compounds in petroleum cuts containing, in particular, aromatic compounds and small quantities of sulphur and/or nitrogen and/or oxygen.
The invention thus relates to a catalyst with a strong hydrogenating phase and moderate acidity. The catalyst comprises at least one group VIII noble metal such as ruthenium, rhodium, palladium, osmium, iridium or platinum. The catalyst also comprises at least one support selected from the group formed by amorphous or low crystallinity supports. The catalyst is characterized in that it also comprises silicon as a doping element. The catalyst can also optionally contain boron, optionally phosphorous, optionally at least one group VIB element, preferably selected from molybdenum and tungsten, and optionally at least one group VIIA element, preferably two group VIIA elements, preferably chlorine and fluorine.
Said catalyst has, for example, an activity for hydrogenation of aromatic hydrocarbons in the presence of sulphur and/or nitrogen and/or oxygen which is higher than known prior art catalytic formulations. Without wishing to be bound to a particular theory, it appears that the improved properties of the catalysts of the present invention are due to reinforcing the acidity of the catalyst by the presence of silicon introduced into the matrix as a dopant. This increased acidity induces a better resistance of the active phase of the catalyst to poisoning by the sulphur and/or nitrogen and/or oxygen and thus improves the hydrogenating properties of the catalyst.
The catalyst of the present invention generally comprises at least one metal selected from the following groups and with the following contents, in weight % with respect to the total catalyst weight:
0.01% to 5%, preferably 0.01% to 2%, of at least one group VIII noble metal, preferably platinum, ruthenium or palladium;
0.1% to 97%, preferably 1% to 95%, of at least one support selected from the group formed by amorphous matrices and low crystallinity matrices, said catalyst being characterized in that it also comprises:
0.1% to 40%, preferably 0.1% to 30%, more preferably 0.1% to 20%, of silicon, (the % being expressed as % of oxides), and optionally:
0 to 20%, preferably 0.1% to 20%, of boron (the % being expressed as % of oxides);
0 to 20%, preferably 0.1% to 15%, more preferably 0.1% to 10%, of phosphorous (the % being expressed as % of oxides);
0 to 20%, preferably 0.1% to 15%, more preferably 0.1% to 10%, of at least one group VIIA element, preferably chlorine and fluorine;
0 to 3%, preferably 0.1% to 3%, of at least one element selected from group VIB, preferably molybdenum or tungsten (the % being expressed as % of oxides).
The noble group VIII metals and the optional group VIB metals in the catalyst of the present invention can be completely or partially present in the form of the metal and/or oxide and/or sulphide.
The catalysts of the invention can be prepared using any suitable method. Preferably, the silicon and optional boron are introduced into the catalyst already comprising the support and the noble group VIII metal or metals. Preferably, a catalyst is impregnated with a solution, for example an aqueous solution, of silicon and optionally by a solution, for example an aqueous solution, of boron (in any order) or it is impregnated with a common solution, for example an aqueous solution, of boron and silicon when the catalyst contain silicon and boron.
More particularly, the process for preparing the catalyst of the present invention comprises the following steps:
a) weighing a solid hereinafter termed the precursor, comprising at least the following compounds: a porous amorphous and/or low crystallinity matrix, at least one noble group VIII element, optionally at least one group VIIA element, optionally phosphorous, optionally boron, and optionally at least one group VIB metal, the whole preferably being formed;
b) impregnating the solid precursor defined in step a) with at least one solution containing silicon;
c) leaving the moist solid in a moist atmosphere at a temperature in the range 10xc2x0 C. to 180xc2x0 C.;
d) drying the moist solid obtained in step c) at a temperature in the range 60xc2x0 C. to 150xc2x0 C.;
e) calcining the solid obtained from step d) at a temperature in the range 150xc2x0 C. to 800xc2x0 C.
The precursor defined in step a) above can be prepared using any conventional methods known to the skilled person.
The silicon, optional boron, optional phosphorous, and optional element selected from group VIIA, the halogens, preferably chlorine and fluorine, can be introduced into the catalyst at various stages of the preparation and in a variety of manners.
The matrix is preferably impregnated using the xe2x80x9cdryxe2x80x9d impregnation method which is well known to the skilled person. Impregnation can be carried out in a single step using a solution containing all of the constituent elements of the final catalyst.
The phosphorous, boron, silicon, and elements selected from the halogens (group VIIA) can be introduced into the calcined precursor by one or more impregnation operations using an excess of solution.
Thus, for example, in the preferred case where the precursor is a platinum-palladium type supported on alumina, it is possible to impregnate this precursor with a Rhodorsil E1P silicone emulsion from Rhxc3x4ne Poulenc, drying at 80xc2x0 C., then calcining at 350xc2x0 C., for example, for 4 hours in dry air in a traversed bed, then impregnating with an ammonium fluoride solution, then drying at 80xc2x0 C., then calcining, for example and preferably in dry air in a traversed bed, for example at 500xc2x0 C. for 4 hours.
Other impregnation sequences can be implemented to obtain the catalyst of the present invention.
Thus in the case where the catalyst contains boron and silicon, it is possible to impregnate first with a solution containing silicon, to dry, to calcine and to impregnate with a solution containing boron, to dry and to carry out a final calcining. It is also possible to impregnate first with a solution containing boron, to dry, to calcine and to impregnate with the solution containing silicon, to dry and to carry out a final calcining. Preferably, it is possible to prepare a solution of at least one boron salt such as ammonium biborate in an alkaline medium and in the presence of hydrogen peroxide and to introduce into the solution a silicone type silicon compound and to carry out dry impregnation, in which the pore volume of the precursor is filled with the solution.
It is also possible first to impregnate the precursor with a solution containing phosphorous, to dry, to calcine then to impregnate the solid obtained with a solution containing boron, to dry and to calcine, and finally to impregnate the solid obtained with the solution containing silicon, to dry and to calcine.
Impregnation of the group VIB element can be facilitated by adding phosphoric acid to ammonium heptamolybdate solutions, which enables phosphorous to be introduced as well, so as to promote the catalytic activity. Other phosphorous compounds can be used, as is well known to the skilled person.
When the elements are introduced in a plurality of steps for impregnating the corresponding precursor salts, an intermediate drying and/or calcining step is generally carried out on the catalyst at a temperature in the range 60xc2x0 C. to 350xc2x0 C.
The catalyst of the present invention comprises a noble group VIII element such as ruthenium, rhodium, palladium, osmium. iridium or platinum, in particular platinum, ruthenium or palladium. Advantageously, the following combinations of metals are used: platinum-palladium, platinum-rhodium, platinum-ruthenium, palladium-rhodium, palladium-ruthenium, rhodium-ruthenium; preferred combinations are platinum-palladium and palladium-ruthenium. It is also possible to use combinations of three metals, for example platinum-palladium-rhodium or platinum-palladium-ruthenium.
The sources of the noble group VIII metals which can be used are well known to the skilled person. Examples are halides, for example chlorides, nitrates, acids such as chloroplatinic acid, and oxychlorides such as ammoniacal ruthenium oxychloride.
A variety of silicon sources can be used. Examples are ethyl orthosilicate Si(OEt)4, silanes, polysilanes, siloxanes, polysiloxanes, and halogenated silicates such as ammonium fluorosilicate (NH4)2SiF6 or sodium fluorosilicate Na2SiF6. Silicomolybdic acid and its salts, and silicotungstic acid and its salts can also advantageously be used. Silicon can be added, for example, by impregnating ethyl silicate in solution in a water/alcohol mixture. Silicon can also be added, for example, by impregnation using a polyalkylsiloxane type silicon compound suspended in water.
The boron source can be boric acid, preferably orthoboric acid H3BO3, ammonium biborate or pentaborate, boron oxide, or boric esters. Boron can, for example, be introduced in the form of a solution of boric acid in a water/alcohol mixture or in a water/ethanolamine mixture.
The preferred phosphorous source is orthophosphoric acid H3PO4, but its salts and esters such as ammonium phosphates are also suitable. Phosphorous can, for example, be introduced in the form of a mixture of phosphoric acid and a basic organic nitrogen-containing compound, such as ammonia, primary and secondary amines, cyclic amines, pyridine group compounds, quinolines, and pyrrole group compounds.
Sources of group VIIA elements which can be used are well known to the skilled person. As an example, fluoride anions can be introduced in the form of hydrofluoric acid or its salts. These salts are formed with alkali metals, ammonium or an organic compound. In the latter case, the salt is advantageously formed in the reaction mixture by reacting the organic compound with hydrofluoric acid. It is also possible to use hydrolysable compounds which can liberate fluoride anions in water, such as ammonium fluorosilicate (NH4)2SiF6, sodium fluorosilicate Na2SiF6 or silicon tetrafluoride SiF4. Fluorine can be introduced, for example, by impregnation using an aqueous hydrofluoride solution or ammonium fluoride or ammonium bifluoride.
Sources of group VIB elements which can be used are well known to the skilled person. Examples of molybdenum and tungsten sources are oxides and hydroxides, molybdic acids and tungstic acids and their salts, in particular ammonium salts such as ammonium molybdate, ammonium heptamolybdate, ammonium tungstate, phosphomolybdic acid, phosphotungstic acid and their salts. Preferably, oxides and ammonium salts are used, such as ammonium molybdate, ammonium heptamolybdate and ammonium tungstate.
The catalyst of the present invention thus also comprises at least one porous mineral matrix which is normally amorphous or of low crystallinity. This matrix is normally selected from the group formed by alumina, silica and silica-alumina. Aluminates can also be selected. Preferably, matrices containing alumina are used, in any of the forms known to the skilled person, for example gamma alumina.
Mixtures of alumina and silica, and mixtures of alumina and silica alumina can advantageously be used.
The catalysts obtained in the present invention are formed into grains of different shapes and dimensions. They are generally used in the form of cylindrical or polylobed extrudates such as bilobes, trilobes, or polylobes with a straight or twisted shape, but they can also be produced and used in the form of compressed powder, tablets, rings, beads or wheels. The specific surface area of the catalysts is measured by nitrogen adsorption using the BET method (Brunauer, Emmett, Teller, J. Am. Chem. Soc., vol. 60, 309-316 (1938)) and is in the range 50 to 600 m2/g. the pore volume measured using a mercury porisimeter is in the range 0.2 to 1.5 cm3/g and the pore size distribution may be unimodal, bimodal or polymodal.
The catalyst of the present invention can be reduced using any method known to the skilled person.
Because of the great sensitivity of noble metals to poisoning by sulphur, it may be appropriate to use a mild catalyst sulphurisation method. Any of the conventional methods which are known to the skilled person can be used. One of those methods consists of exposing the catalyst to a very light feed such as a white spirit to which a sulphur-containing compound such as dimethyldisulphide has been added. The catalyst is then sulphurised at a temperature in the range 100xc2x0 C. to 800xc2x0 C., preferably 150xc2x0 C. to 600xc2x0 C.
More particularly, the catalyst of the present invention can be used for hydrogenation of aromatic compounds or for dearomatisation, or for reducing the aromatic compound content of petroleum cuts containing, in particular, aromatic compounds and small quantities of sulphur and/or nitrogen and/or oxygen.
The feeds used in the process are aromatic feeds generally containing less than 2000 ppm by weight of sulphur, less than 1000 ppm by weight of nitrogen, less than 1000 ppm by weight of oxygen, a portion of which can be present in the form of water. These feeds have generally already been hydrorefined to reduce the sulphur, nitrogen and oxygen contents. They may be gasolines, kerosines, gas oils from distilling a crude oil or feeds such as vacuum gas oils, or deasphalted or non deasphalted distillation residues, which may or may not have already been refined. The treated feeds are feeds with an initial distillation point of more than 80xc2x0 C. and less than 580xc2x0 C.
The hydrorefining conditions such as temperature, pressure, hydrogen recycle ratio, and hourly space velocity, can vary widely depending on the nature of the feed, the quality of the desired products and the facilities available to the refiner. The temperature is generally over 150xc2x0 C. and usually in the range 200xc2x0 C. to 320xc2x0 C. The pressure is over 0.1 MPa and usually in the range 1.5 to 10 MPa. The hydrogen recycle ratio is a minimum of 10 and usually in the range 20 to 2000 normal liters of hydrogen per liter of feed. The hourly space velocity is generally in the range 0.1 to 40 volumes of feed per volume of catalyst per hour, preferably in the range 0.1 to 10. The results which are of interest to the refiner in this case are the aromatic compound hydrogenation activity.
The following examples illustrate the present invention without in any way limiting its scope.